Grinding machine



Sept. 20, 1949; P. H. H'lJTi-MSON 2,482,485

GRINDINGF MACHINE Filed May 17, 1945 2 Sheets-Sheet 1 F i g. l

[00 Qia-A f H/s ATTORNEY Sept. 20, 1949K. P. H. HuTcHlNsoN GRINDING MACHINE 2 Sheets-Sheet 2 Filed May 1'7, 1945 lnvpNTp: PH/L/P H. HuT'cH//vso N,

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Parente-sepa 2o, 1949 GRINDING MACHINE Philip Hutchinson, Montclair, N. J assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application May 17, 1945, Serial No. 594,199

26 Claims.

This invention relates to grinding machines and comprises all of the features of novelty herein disclosed. An object of the invention is to provide an improved machine for grinding spherical ends on round articles. Another object is to so grind tapered rollers that spherical ends will be produced at a predetermined and unvarying distance from the apices of the tapering surfaces.

To these ends and also to improve generally upon devices of this character, the invention consists in the various matters hereinafter described and claimed. In its broader aspects the invention is not necessarily limited to the specific construction selected for illustrative purposes in the accompanying drawings in which Fig. 1 is a front elevation with the wheel heads in vertical section and with parts removed.

Fig. 1A is an enlarged sectional view of parts near the middle of Fig. 1.

Fig. 2 is a sectional view of the grinding wheel head and associated parts.

Fig. 3 is a front elevation of a portion of Fig. 1 with the loading and discharge mechanism added.

Fig. 4 is a side view of Fig. 3 with a grinding wheel in section and with the right hand wheel head removed.

Fig. 5 is a plan view of a loading block.

Fig. 6 is a perspective view of a wiper shoe and its mounting.

Fig. '1 is a view similar to a portion of Fig. 4 but having a grinding wheel and feed disc in operative relation to rollers having ends ofv a larger radius.

Fig. 8 is a section view to larger scale vof the loading block and associated mechanism.

In the usual tapered roller bearing, the rollers and the races taper towards a common point in the axis of the bearing, the larger ends of the rollers engaging a thrust iiange on the inner race ring. It is important that these .larger ends all terminate at the same distance from that common point which is the apex of the tapered surfaces in order that all rollers may carry equal thrust load and be properly guided by the thrust flange. According to this invention the large ends are ground to lie in a spherical surface which has its center at the common point. The rollers are rotated on their axes while these axes intersect at a common point, the ends of the rollers being traversed across a concave spherical surface whose center of curvature is at that common point. The rollers are maintained at the proper distance from the center of curvature by engagement of their tapered surface with a pair of oppositely rotating wheels having similarly tapered surand 6 which provide slideways for slidable heads 8 and l0 respectively, each head having an adjusting screw I2. 'I'he block 6 is pivoted at I4 and has a projection I8 extending between a pair of screws l8 threaded in lugs 20 on the frame. This is to provide for accurately aligning the two heads. A bracket 22 is fastened to the top of each head and a screw rod 24 is pivoted to one bracket to swing Vdown into a fork in the other, a nut 26 being threaded on the rod to engage the adjacent bracket. This is to brace the heads and prevent spreading. 0n the top of each head is a motor 28 having step-down gearing which drives a gear 30 fastened to a spindle journalled in each head, the spindles turning comparatively slowly in opposite directions at somewhat diiferent speeds.

The left hand spindle 32 is solid and carries a wheel 34 arranged in opposition to a similar wheel 36 on the right hand spindle 38 which is hollow. Each spindle has near the outer end a pair of ball bearings 40 whose inner race rings are clamped faces which are held at a predetermined and un- Varying distance apart.` The rollers are held from y skewing out of a radial position by a feed disc being slidable in the head. A thrust ball bearing 48 is interposed between a shoulder in the head and a thrust collar on the spindle. An angularA guard 50 is fastened to a flange on the spindle and extends axially to overlap a drain groove 52 on the head. Inside of the guard 50, an internally bevelled washer 54 is urged' axially by springs against a mating externally bevelled washer 56 which is fastened to the head. Washer 54 is preferably made of bronze and its mating washer of steel.

The right hand spindle 38 is hollow and journalled therein is a shaft 62 which isl driven by a sprocket wheel 64 at a speed which is one half the difference in speed between the wheels 34 and 36. It turns in the direction of the faster wheel. The shaft 62 is journalled near one end in a roller bearing 66 and near the other end in a ball bearing 68. The outer race ring of the ball bearing is clamped in the spindle 38 by a sealing washer 18 Whose fastening screws are accessible through holes in a flange 12 on the shaft. Fastened to the flange 12 by screw bolts is-a feed disc or article holder 14 which is centrally apertured to be 'centered on a flanged centering plug 15 carried by the shaft.

The feed disc 14 has a series of pockets formed by notches 16 in the periphery, the sides of each notch making the same angle as that included by the tapered rollers T. The notches prevent skewing of the rollers out of a radial position. The adjacent portionsof the wheels have tapered or conical surfaces 18 which include the same sans angle as the rollers. The apices of these angles are located in the aligned axes of the two spindles. The rollers radially protrude from the notches but are held on four sides so that their axes must intersect at the aligned axes of the two spindles. The feed disc projects slightly beyond the wheels and carries a dressing diamond 80 at a distance from the center equal to the radius to be generated on the ends of the tapered rollers.

A grinding wheel G is removably secured to a flange 84 on a hollow spindle 36 which is driven by -a pulley 66 and a belt from a motor (not shown) mounted on a head or slide 60. The spindle is journalled on antifriction bearings similar to those previously described. A pipe 92 extends through the spindle, being non-rotatably supportedinabushinguatoneendandina threaded sleeve 66 threaded in the spindle beyond a packing structure 36. A valve |60 controls supply of liquid to the pipe which discharges through a central passage |62 in the grinding wheel. This passage may be quite large since the surface speed of the wheel is lower near the center. The illustrated wheel is dressed as a segment of a sphere, conveniently referred to as of spherical shape, the spherical surface |04 having the radius to be reproduced on the ends of the tapered rollers. The dressing diamond on the feed disc 14 keeps the wheel in shape.

The head or slide 36 is adjustable at right angles to the spindles 32 and 36 by a screw |06 threaded in a nut |06 fastened to a block ||0 on the frame. The screw is journalled in a bracket ||2 on the slide and is turned by suitable ratchet mechanism including a ratchet wheel ||4 actuated by a pawl (not shown) on a pawl carrying lever I |6 which is oscillated, as by a solenoid energized at desired intervals. The axis of the grinding spindle intersects the extended and aligned axes of the wheel spindles. .'I'he slide 90 is located so that the spherical surface of the grinding wheel will everywhere be equidistant from the aligned axes of the spindles 32 and 36 and the slide is fed at intervals to compensate for wheel wear and dressing,

The rollers are fed one by one into the notches of the feed disc from a flexible feed chute |20 connected to a loading sleeve |22 whose lower end has axial slits |24 at four sides. The sleeve is secured by a set screw in a hole'in a block |26 having a tongue |23 guided in a nearly vertical groove I2! to grind larger rollers TI.

plate has a tongue guided in a horizontal groove |48 on this bracket which has a horizontal series of tapped openings for securing screws. A coil spring |50 is anchored to a pin on the plate |40 and to an adjusting screw |52 threaded in the nead of a pin |54 which is swivelled in an opening of the arcuate arm. After the rollers are traversed over the grinding wheel they pass under a spring-pressed exit shoe |56 similar to the entrance shoe |38 and adjustably mounted in a similar manner on the left hand head. The shoe is on an arcuate arm |58 pivoted to a horizontally adustable bracket |60 and urged upwardly by a coil spring |62.

The rollers are'free to drop from the `notches into a suitable receptacle or chute after they pass the exit shoe but to insure discharge a stripper |64 is-employed. The stripper is a comparatively thin blade which projects horizontally between one of the wheels and the disc 14 to a point where the lower edge |66 will act as a cam to engage the inner or small ends of the rollers and expel them. The stripper is fastened at a point beyond the wheels to the side of an angle bracket |60 whose base is slotted and adjustable in a direction parallel to the spindles, the base having a tongue |10 guided in a groove of a supporting block |12 on the main frame, Ihe disc 14 need not be exactly half way between the wheels 34 and 36 but may be slightly displaced laterally to make more room for the stripper. Adjusting the wheels farther apart for larger diameter rollers increases the space between the disc and the left hand wheel without changing the distance between the disc and the other wheel.

The vario adjustments on the machine provide for the grinding of rollers of different sizes without replacing many parts. The radius of the concave grinding surface |04 depends on the desired radius of the end face of the tapered roller. The larger this radius, the larger will be the wheels 34 and 36 and the disc 14. Fig. I indicates a disc 14A larger than the disc 14 to cooperate with a grinding wheel GI having a radius Ri For smaller rollers, tl grinding wheel G2 would have a radius R2, e

The angle made by the conical or outwardly flared roller contacting surfaces 18 and the angle 50 made by the notches on the feed disc depends on on the right hand bracket 22, the block having a slotted bracket portion |36 by means of which it can be secured to the head in selected positions depending on the radius of the wheels. The block |26 has a pipe connection at |32 leading to a port' |33 to supply fluid to an annular groove |34 and inclined ports |36 inthe loading sleeve, thus to expel the tapered rollers small end foremost into the notches of the feed disc. The lowest roller in the feed tube rides on the disc 14 until a notch 16 arrives to receive it. The slits at |24 allow the expelling fluid to escape freely.y

As the rollers are'carried to the grinding wheel, they are wiped to fully seated position against the tapered surfaces 'I3 and in the notches by a spring-pressed entrance shoe |36 which rides on the peripheries of the wheels 34 and 36 or on the ends of the rollers. the shoe having a groove |46 which receives the ends of the rollers and is inclined in a direction to urge the rollers into their seats. 'I'he shoe is swivelled by a pin |4| to the side of an arcuate arm |42 which is pivoted at |44 to a plate |46 whichis horizontally slotted the included angle of the tapered rollers. The wheels 34 and 36 can be adjusted towards or from one another by their slides to accommodate rollers of different diameter but once adiusted are maintained in non-spreading spaced relation so that the rollers are limited in radial movement towards the axis of the wheels by the opposed tapering surfaces 10 which are maintained at a predetermined and unvarying distance apart. Consequently the spherical ends to be ground will all have a definite predetermined radius which has a center of curvature at the wheel axes. The rollers have a slight clearance in the notches for free rotation.

The relation of the end spherical surfaces to the roller diameter and to the apex of the included angle is predetermined and this is important in the operation of the rollers in a tapered roller bearing wherein the spherical ends are guided by a flange on one of the race rings and wherein this flange should come into guiding action when all the rollers and opposing raceways are in proper, equal load taking positions. By definitely locating the spherical end face to the and adjustable on the left hand bracket 22. The diameter and to the apex of the included angle.,

this desired action is insured in contrast to a roller which might have its end face stick out too far or not enough with respect to its maximum diameter and apex. In thepresent invention, a little extra, length at the small end of a roller would be immaterial.

Without limiting the invention, it may be stated that it is satisfactory to make the wheel 34 rotate at about 46 R. P. M., the wheel I6 at about 50 R. P. M., and the disc 14 at about 2 R. P. M., the latter speed being one half the difference in speed of the wheels and the disc turning in the direction of the faster wheel. The grinding wheel is driven at usual grinding speed. The wheels 34 and 36 constitute rotary driving elements which frictionally turn the rollers on their axes and thereby urge them to travel bodily across the concave grinding surface. The wheels also constitute rotary pressure members with outwardly flared roller contacting surfaces which tend to wedge the rollers outwardly.

I claim: p

1. In a machine for grinding spherical ends on .tapered rollers, a grinding wheel having a concave grinding surface, a pair of work rotating wheels having their axes in a line passing through the center of curvature of the grinding surface, the work rotating wheels having opposed tapering surfaces to engage opposite sides of the tapered rollers, the tapering surfaces making the same angle with one another as the included angle of the tapered rollers, means for rigidly holding said work rotating wheels at a predetermined and unvarying distance apart `to maintain a fixed relation of their tapering surfaces, and means to maintain the rollers radially with respect to the aligned axes of the work rotating wheels as the ends of the rollers traverse the grinding surface.

2. In a machine for grinding spherical ends on tapered rollers, a grinding wheel having a concave grinding surface, a pair of work rotating wheels having their axes in a line passing through the center of curvature of the grinding surfacel the work rotating wheels having opposed tapering surfaces to engage opposite sides of the tapered rollers, the tapering surfaces making the same angle with one another as the included angle of the'tapered rollers, means for rigidly holding said work rotating wheels at a predetermined and unvarying .distance apart to maintain a fixed relation of their tapering surfaces, and a driven member between the tapering surfaces and having outwardly open notches to receive the rollers, the sides of each notch making the same angle as the included angle of the rollers.

3. In a machine for grinding spherical ends on .tapered rollers, a grinding wheel having a concave grinding surface, a pair of work rotating wheels having their axes in a line passing through the center of curvature of the grinding surface, the work rotating wheels having opposed tapering surfaces to engage opposite sides of the tapered rollers, means for rigidly holding said work rotating wheels at a predetermined and unvarying distance apart, and a feed disc between the wheels and having 4outwardly open notches,

the opposite sides of the notches and the opposed tapering surfaces of the wheels receiving the rollers therebetween and holding them on four sides with their axes intersecting at said center of curvature.

4. In a machine for grinding spherical ends 6 on tapered rollers, a grinding wheel having a concave grinding surface, a pair of work rotating wheels having their axes in a line passing through the center of curvature of the grinding surface, the work rotating wheels having opposed tapering surfaces to engage opposite sides of the tapered rollers, means for rigidly holding said work rotating wheels at a predetermined and unvarying distance apart so that their tapered surfaces positively limit movement of the rollers radially of the work rotating wheels, means for rotating said wheels in opposite directions at diierent speeds, a feed disc between the wheels to hold the rollers radially ofthe wheels while carrying the ends of the rollers along the grinding surface, and means for rotating the disc at one half the difference in speed of the work rotating wheels.

5. In a machine for grinding spherical ends on tapered rollers, a grinding wheel having a concave grinding surface, mechanism for traversing the ends of the rollers along the grinding surface while rotating the rollers on axes which always intersect at the center of curvature of the grinding surface, said mechanism comprislng a rotating disc having roller receiving notches with tapering sides, and a pair of oppositely moving tapered surfaces fitting against opposite sides of the rollers and maintained at a predetermined and unvarying distance apart to prevent axial movement of the rollers towards said center of curvature.

6. In a machine for grinding spherical ends on tapered rollers, a grinding wheel having a concave grinding surface, mechanism for traversing the ends of the rollers along the grinding surface while rotating the rollers on axes which always intersect at the center of curvature of the grinding surface, said mechanism comprising a rotating disc having its periphery provided with outwardly open roller receiving notches whose side walls intersect at the center of curvature of the grinding surface, and a pair of oppositely rotating wheels having tapered surfaces fitting opposite sides of the rollers and held in unvarying spaced relation to determine the radial distance of the rollers from said center of curvature. Y

7. In a machine for .grinding spherical ends on tapered rollers, a grinding wheel having a spherical grinding surface, mechanism for traversing the ends of the rollers along the spherical grinding surface while rotating the rollers on axes which always intersect at the center of curvature of the spherical grinding surface, said mechanism comprising a pair of oppositely rotating wheels having tapered surfaces iltting opposite vsides of the rollers and held in unvarylng spaced relation to determine the radial distance of the rollers from said center of curvature, and means rotatable between the pair of wheels and engaging the tapered surfaces of the rollers for 'preventing the rollers from skewing out of a radial position as their ends are traversed across and ground oiI by the grinding surface.

8. Ina machine for grinding spherical ends on rollers, a grinding wheel having a spherical grinding surface, mechanism for traversing the ends of the rollers along the spherical grinding surface while rotating the rollers onaxes which always intersect at the center of curvature of the spheical grinding surface, said mechanism comprising a pair of oppositely rotating wheels to engage opposite sides of the rollers and a ro- 7 tatable disc having roller receiving pockets between the wheels, and the disc having a dressing tool at its periphery to traverse thev grinding surface while the rollers are also traversed over the grinding surface.

9. In a machine for grinding spherical ends on rollers, a grinding wheel having a concave grinding surface, a pair of work rotating wheels having driving spindles, one of said spindles being hollow, a shaft extending through said hollow spindle, a feed disc on said shaft between the'wheels and having roller receiving pockets, means for driving the spindles in opposite directions at different speeds, and means for driving the shaft in the direction of the faster spindle at a speed which is one half the diiference in spindle speeds.

10. In a machine for grinding the ends of rollers', a grinding wheel having a spherical grinding surface, a pair of work rotating wheels 4to engage ODDOSite sides of the rollers, a feed disc between the wheels and having pockets for the rollers, and a spring pressedshoe overlying the disc at a location adjacent to the spherical grinding surface to urge the rollers against the work rotating wheels to start rotation of the rollers before they enter within and engage the spherical grinding surface.

ll. In a machine for grinding the ends of rollers, a grinding wheel, a pair of rotating wheels to engage opposite sides of the rollers, a rotatable disc having roller` receiving pockets between the wheels and open outwardly, a loading sleeve arranged substantially radially of said disc `to direct rollers towards said pockets. and means for creating fluid pressure in the sleeve to expel a roller into one of the pockets. s

12. In a machine for grinding the ends of rollers, a grinding wheel having a concave grinding surface, mechanism for carrying the rollers across the grinding surface while their axes are held radially to always intersect the center of curvature of the concave grinding surface, said mechanism comprising oppositely rotating wheels and a rotating feed disc, the disc having its axis intersect said center of curvature and having outwardly open pockets for the rollers, and a roller engaging shoe overlying the disc and arranged substantially tangent to the concave grinding surface to hold the rollers against outward movement with respect to the oppositely rotating wheels to insure rotation of the rollers before they enter within and engage the concave grinding surface.

13. A machine for end-grinding elongated articles comprising a rotary grinder, a rotary article holder thinner than said articles and having peripheral article holding recesses open laterally to expose the sides of said articles, said rotary article holder being positioned to'move the ends of said articles across said grinder, means engageable with the exposed sides of said articles for rotating said articles around their longitudinal axes while being moved across said grinder. and means for urging said articles outwardly of said holder while so rotating them.

14. A machine for end-grinding elongated articles comprising a rotary grinder, a rotary article holder thinner than said articles and having peripheral article holding recesses open laterally to expose the sides of said articles, said rotary article holder being positioned to move the ends of said articles across said grinder, a rotary driving element mounted on one side of said article holder and engageable with the exposed sides of said articles for rotating said articles around their longitudinal axes while being moved across said v grinder, a rotary pressure m'ember mounted on the other side of said article holder and engaging the opposite sides of said articles for ursins them into engagement with said driving element, a power source, `and power-transmitting mechanism drivingly and rotatively connecting said rotary holder and said rotary driving element to said power source. Y

l5. A machine for end-grinding tapered rollers comprising a rotary grinder, a rotary rollerl hold- 'er positioned to move the ends of said rollers across said grinder and having peripheral recesses for receiving said rollers, said recesses being open laterally to expose the sides of said rollers, a rotary driving element mounted on one side of said roller holder and engageable with said exposed sides for rotating said rollers while being moved across said grinder, a rotary pressure member mounted on the other side of said article holder and urging said rollers into driven engagement with said driving element, said rotary grinder being mounted for rotation upon an axis transverse to the axes of rotation of said roller holder, said driving element Vand said pressure member, a power source and power-transmitting mechanism driving and -rotatively connecting said rotary holder and said rotary driving element to said power source.

16. A machine for end-grinding tapered rollers comprising a rotary grinder, a rotary roller holder positioned to move the ends of said rollers across said grinder and having peripheral recesses for receiving said rollers, said recesses being open laterally to expose the sides of said rollers. a rotary driving element engageable with said exposed sides for rotating said rollers while being moved across said grinder, a power source, and power-transmitting mechanism drivingly and rotatively connecting said rotary holder and said rotary driving element to said power source, said mechanism being proportioned and arranged to rotate said driving element more rapidly than 4s said holder thereby tending to urge said rollers comprising a rotary grinder, a rotary roller holder positioned to move the ends of said rollers across said grinder and having peripheral recesses for receiving said rollers, said recesses being open laterally to expose the sides of said roll- 55 ers, a rotary drivingelement engageable with said exposed sides for rotating said rollers while being moved across said grinder, and a rotary pressure member engaging the opposite sides of said rollers for urging said rollers into engage- .o ment with said driving element, said driving element and said pressure member having outwardly ilared roller contacting surfaces whereby to urge said rollers outwardly of said recesses during the rotation of said holder.

18. A machine for end-grinding tapered rollers comprising a rotary grinder, a rotary roller holding wheel positioned to move the ends `of said rollers across said grinder and having peripheral recesses for receiving said rollers, said recesses being open laterally to expose the sides of said rollers, a rotary driving wheel engageable with said exposed sides for rotating said rollers while being moved across said grinder, and a rotary pressure wheel mounted on the opposite side of said roller holding wheel from said driving wheel and also engaging the exposed sides of said rollers, andmechanism for positively driving at least two of said wheels.

19. A machine for end grinding elongated articles comprising a rotary grinder, a rotary article holder positioned to move the ends of said articles across said grinder, rotary driving elements disposed on opposite sides of said article holder in driving engagement with the opposite sides of said articles, and means for driving said driving elements in opposite directions at different peripheral speeds thereby tending to impart a resultant rotation to said rotary article holder.

20. A machine for end-grinding tapered rollers comprising a rotary grinder, a rotary roller holder positioned to move the ends of said rollers across said grinder and having peripheral recesses for receiving said rollers, said recesses being open laterally to expose the sides of said rollers, a rotary driving element engageable with said exposed sides for rotating said rollers while being moved across said grinder, a rotary pressure member engaging the opposite sides of said rollers for urging said rollers into engagement with said driving element, and means for tilting the axis of rotation of said pressure member relatively to the axis of rotation of said holder whereby to provide a space wider than said rollers remote from said grinder for receiving said rollers and also to urge said rollers outwardly of said recesses during the rotation of said holder.

21. A machine for end-grinding tapered rollers comprising a rotary grinder, a rotary roller holder positioned to move the ends of said rollers across said grinder and having peripheral recesses for receiving said rollers, said recesses being open laterally to 'expose the sides of said rollers, a rotary driving element engageable with said exposed sides for rotating said rollers while being moved across said grinder, and a rotary pressure member engaging the opposite sides of said rollers for urging said rollers into engagement with said driving element, said driving element and said pressure member having outwardly liared roller contacting surfaces, and said pressure member having its axis of rotation tiltable forwardly relatively to the axis of rotation of said holder whereby to provide a space wider than said rollers remote from said grinder for receiving said rollers and also to urge said rollers outwardly of said recesses during the rotation of said holder.

22. A machine for end grinding elongated articles comprising a rotary grinder, a rotary article holder mounted for rotation and positioned to move the ends of said articles across said grinder, rotary driving elements disposed on opposite sides of said article holder in driving engagement with the opposite sides of said articles, and means for driving said driving elements in opposite directions at different peripheral speeds thereby tending to impart a resultant rotation to said rotary article holder.

23. A machine for end grinding elongated articles comprising a rotary grinder, a rotary article holder mounted for rotation and positioned to move the ends of said articles across said grinder, rotary driving elements disposed on opposite sides of said article holder in driving engagement with the opposite sides oi' said articles. and means for driving said driving elements in opposite directions at different peripheral speeds thereby tending to impart a resultant rotation to said rotary article holder, said article holder having spaced peripheral recesses therein for receiving and holding -said articles.

24. A machine for end grinding elongated articles comprising a rotary grinder, a rotary article holder mounted for rotation and positioned to move the ends of said articles across said grinder, rotary driving elements disposed on opposite sides of said article holder in driving engagement with the opposite sides of said articles, and means for driving said driving elements in opposite directions at different peripheral speeds thereby tending to impart a, resultant rotation to said rotary article holder, said -article holder having spaced peripheral recesses open at the opposite sides thereof to expose the sides of said articles to engagement by said rotary driving ele-` ments.

25. A machine for end grinding elongated articles comprising a rotary grinder, a rotary article holder mounted for rotation and p0sitioned to move the ends of said articles across said grinder, rotary driving elements disposed on opposite sides of said article holder in driving engagement with the opposite sides of said articles, and means for driving said driving elements in opposite directions at different peripheral speeds thereby tending to impart a resultant rotation to said rotary article holder, said article holder having spaced peripheral recesses therein for receiving and holding said articles, said rotary driving elements having oppositely and outwardly ared article contacting surfaces whereby to urge said rollers outwardly of said recesses during the rotation of said article holder.

26. The method of grinding spherical ends on tapered rollers to a prescribed radius of curvature and constant distance from the apex of the included angle, which consists in supporting the rollers for frictional contactwith opposed conical surfaces, maintaining the spacing of the elements of the conical surfaces so that they always intersect at a common apex at the center of curvature of a. concave grinding surface, maintaining the rollers from skewing between the conical surfaces and with their axes always pointing to the said common apex, and relatively rotating the conical surfaces'around their axes to turn the `rollers on their axes and traverse their large ends across the concave grinding surface.

PHILIP H. HUTCHINSON.

4 REFERENCES CITED The following references are of record in the Ille of this patent:

UNI'I'ED STATES PATENTS Number Name Date 613,934 Norton Nov. 8, 1898 1,055,043 Hirth Mar. 4, 1913 1,061,241 Hirth May 6, 1913 1,261,157 Norton Apr. 2, 1918 1,298,486 Fjellman Mar. 25, 1919 1,383,941 Harman July 5, 1921 1,384,756 -Hambuechen July 19, 1921 1,662,241 Drake Mar. 13, 1928 2,024,118 Vanderbeek Dec. 10, 1935 2,341,825 Spicacci Feb. 15. 1944 

